1. Field of the Invention
The present invention relates to an ink jet recording apparatus for recording by discharging ink from recording means onto a recording medium.
2. Related Background Art
A recording apparatus having the feature of a printer, a copying machine, or a facsimile apparatus, or a recording apparatus for use as the output device from complex electronic equipment including a computer or word processor, or a work station is constituted to record an image onto a recording sheet (recording medium) such as a paper or plastic thin plate, based on image information. Such recording apparatuses can be classified as ink jet systems, wire dot systems, thermal systems and laser beam systems.
In a recording apparatus of the serial type based on the serial scan method of scanning in a direction transverse to a conveying direction (sub-scan direction) of a recording medium, recording is performed on the recording medium by repeating an operation of recording (or scanning) the image with recording means (typically mounted on a carriage) movable along the recording medium, after setting the recording medium at a predetermined recording position, feeding a sheet (or conveying the recording medium) by a predetermined amount after terminating the recording of one line, and then again recording (or scanning) the image at the next line on the recording medium which is stopped. On the other hand, in a recording apparatus of the line type in which the recording is conducted only by sub-scanning in a conveying direction of the recording medium, recording is performed on a recording medium by repeating an operation of setting the recording medium at a predetermined recording position, recording one line collectively, feeding a sheet (or conveying the recording medium) by a predetermined amount, and further recording the next line collectively.
Among the above recording apparatuses, a recording apparatus of the ink jet system (an ink jet recording apparatus) performs recording by discharging the ink from recording means (recording head) onto a recording medium, having the advantages in which the recording means can be made compact, a high definition image can be recorded at a high speed, the ordinary paper is usable for recording without needing of any special treatment, the running cost is low, little noise is produced owing to the non-impact method, and the color image is easily recorded by using color inks. And a line-type, recording apparatus using recording means of the line type in which a number of discharge ports are arranged in a direction of the sheet width, allows for a higher speed recording.
In particular, recording means (recording head) of the ink jet system of discharging the ink by the use of heat energy can be easily fabricated with an arrangement of liquid channels (discharge ports) at a high density by forming electricity-heat converters, electrodes, liquid channel walls, and a ceiling plate as the film on a substrate through a semiconductor fabrication process such as etching, vapor deposition or sputtering, thereby allowing for a more compact configuration. On the other hand, there are a variety of requirements for the material of which the recording medium is composed, and in recent years, besides a paper or resin thin plate (e.g., OHP) which is an ordinary recording medium, the use of a thin paper or processed paper (punched paper for filing, scored paper, or any shaped paper) has been demanded.
In the above-described ink jet recording apparatus, capping means is used to enclose a discharge port area so that discharge ports are shielded from the outside, in order to prevent the occurrence of clogging due to the increase of viscosity or fixedly deposited ink produced by the drying of ink around the discharge port area of the recording means (recording head), or a suction recovery operation of compulsorily discharging the ink through discharge ports is enabled by applying a predetermined pressure (including a negative pressure) to the discharge port in order to remove (or dissolve) the clogging caused by thickened or fixed ink, bubbles or dirt within liquid channels.
The capping means is arranged to seal the discharge port by making contact with the recording head at a position outside of the recording region (e.g., a home position of the recording head or carriage). The operation mechanism for this capping means may involve for example, moving a cap attached to a cap holder so as to make contact with the recording head by utilizing the movement of the recording head (or carriage), or advancing a cap attached on a movable cap holder so as to make contact with the recording head stopped at a predetermined position.
The above mechanism utilizing the movement of the carriage is configured in such a way that the cap holder is movably attached to holder guide (guide member) by cam means, the approaching carriage (or recording head) is caused to engage the cap holder, and the cap holder is moved toward the recording head by using a further movement of the carriage so as to place the cap into close contact with the discharge port formation face.
By the way, the contact portion of the cap at least with the recording head is made of a rubber elastic material (elastic member) to insure the sealing performance more securely. Also, the cap is connected with one end of a tube via a tube connector, the other end of the tube being connected to a suction pump, which is connected via a tube to a waste ink treating member (e.g., ink absorbing member). Thus, if a discharge failure occurs due to the clogging of the discharge port, a suction recovery operation is carried out in which the cap is brought into contact with the discharge port formation face, and then the ink is compulsorily discharged through discharge ports by applying a predetermined pressure (negative pressure) to the discharge port by means of the suction pump. To resume the recording after the suction recovery operation, the cap holder is caused to move in a direction of retracting (or separating) from the recording head, and the carriage is caused to move to the recording region if the head is of the serial type.
However, in a conventional ink jet recording apparatus, when capping the recording head with a cap made of elastic material, the cap holder may be positioned inclinedly with respect to a cap contact face (discharge port formation face) of the recording head, due to a bending reaction of the tube (such as an elastic restoring force tending to restore the bent tube to its original state), or a dimensional or mounting tolerance existing in a positioning part of the cap holder for the capping, the positioning part being located between a main body base and the holder guide (or cap holder), and a cam engaging part being located between the holder guide and the cap holder, so that the amount of penetration may vary at various portions of the cap to cause a deformation at a contact portion of the cap with the discharge port formation face, leading to a capping failure and leakage. In particular, in a recording apparatus provided with a plurality of recording heads (head elements), the amount of penetration of the cap may be different between recording heads, resulting in the higher possibility of producing the capping failure with the recording head.
If leakage occurs in the cap, the ink may be thickened or fixed so that the clogging of discharge port is likely to occur, because the discharge ports are not completely shielded from the outside air. Also, at the time of the suction recovery operation, a predetermined suction force (negative pressure) may not be obtained at the discharge port due to the leakage, so that the suction recovery can not be performed. As a countermeasure, for example, when a problem associated with the inclined positioning of the cap is caused by the bending reaction of the tube, it is contemplated to avoid the bending reaction of the tube exerting on the cap by increasing the bend radius (R) of tube by the use of a longer tube, but such a constitution has the problem of requiring more space for disposing the tube, resulting in a larger recording apparatus. Because of the increased volume of tube extending from the suction pump to the cap, there is a problem that the suction force (strength of negative pressure) becomes insufficient if using the same pump, in which in order to apply the same suction force to the discharge ports, a larger pump is required, which produces a higher cost.
Also, when a problem is caused by the dimensional or mounting tolerance in a component of the cap means, a method of adjusting the inclination of the cap holder by using a movable positioning part of holder guide has been proposed, but this method is associated with a problem of bringing about the higher price, with reduced handling capability, because of the higher costs, a larger apparatus, and the addition of an adjusting process, which are caused by the increase in the number of components.